For anyone having major issues using bluetooth headphones since updating to win 10 v1903, it is a known issue. There is a partial fix.
If you have intel bluetooth on your machine, you must update to this driver:
And also disable the 'headset' portion of your bluetooth headphones in sound manager, as well as all other mic input devices. Once this is done, your bluetooth headphones will work again in games instead of immediately muting when the game is launched.
There is presently no fix to allow you to use bluetooth headphones as a mic if they are set up as 2 seperate devices (headphones/headset).
For non-intel bluetooth, you would be best served seeking out the latest driver version for your hardware and updating. This issue is recognised by microsoft to the point that v1903 is not rolling out through official channels to those with as yet unsupported bluetooth driver on their machines.
Thank you to teamos for this excellent release. Very stable, very clean, great performance.